This invention relates to novel froth flotation frothers which demonstrate enhanced recovery of fine particles of coal in froth flotation.
Froth flotation is a commonly employed process for concentrating minerals from ores and coal values from raw coal. In a flotation process, the ore or raw coal is crushed and wet ground to obtain a pulp. A frothing agent, usually employed with a collecting agent, is added to the ore or raw coal to assist in separating valuable minerals or coal from the undesired or gangue portions of the ore or raw coal in subsequent flotation steps. The pulp is then aerated to produce a froth at the surface thereof and the collector assists the frothing agent in separating the mineral or coal values from the ore or raw coal by causing the mineral or coal values to adhere to the bubbles formed during this aeration step. The adherence of the mineral or coal values is selectively accomplished so that the portion of the ore or raw coal not containing mineral or coal values does not adhere to the bubbles. The mineral- or coal-bearing froth is collected and further processed to obtain the desired mineral or coal values. That portion of the ore or raw coal which is not carried over with the froth, usually identified as "flotation tailings", is usually not further processed for extraction of mineral or coal values therefrom. The froth flotation process is applicable to ores containing metallic and nonmetallic mineral values and to coal.
In flotation processes, it is desirable to recover as much coal or mineral values as possible from the raw coal or ore while effecting the recovery in a selective manner, that is, without carrying over undesirable portions of the raw coal or ore in the froth.
While a large number of compounds have foam or froth producing properties, the frothers most widely used in commercial froth flotation operations are monohydroxylated compounds such as C.sub.5-8 alcohols, pine oils, cresols and C.sub.1-4 alkyl ethers of polypropylene glycols as well as dihydroxylates such as polypropylene glycols. The frothers most widely used in froth flotation operations are compounds containing a nonpolar, water-repellent group and a single, polar, water-avid group such as hydroxyl (OH). Typical of this class of frothers are mixed amyl alcohols, methylisobutyl carbinol, hexyl and heptyl alcohols, cresols, terpineol, etc. Other effective frothers used commercially are the C.sub.1-4 alkyl ethers of polypropylene glycol, especially the methyl ether and the polypropylene glycols of 140-2100 molecular weight and particularly those in the 200-500 range. In addition, certain alkoxyalkanes, e.g., triethoxybutane, are used as frothers in the flotation of certain ores.
Although mineral or coal value recovery improvements from a preferred frother in the treatment of an ore or raw coal can be as low as only about 1 percent over other frothers, this small improvement is of great importance economically since commercial operations often handle as much as 50,000 tons of ore or raw coal daily. With the high throughput rates normally encountered in commercial flotation processes, relatively small improvements in the rate of mineral or coal recovery result in the recovery of additional tons of mineral or coal values daily. Obviously then, any frother which promotes improved mineral or coal value recovery, even though small, is very desirable and can be advantageous in commercial flotation operations.
It is well-known in the practice of froth flotation, that the recovery of fine (slime) particles of coal with reasonable selectivity toward the valuable coal over the gangue (ash) is quite difficult. Normally the problem is not one of achieving high recovery of the valuable component, but rather one of accepting much lower than desired valuable recovery so as to achieve a fines valuable product of an acceptable quality or grade (selectivity). In practice, it is normally found that as the valuable recovery of fines is increased, the quality of the flotation product (selectivity) dramatically decreases. Thus, an economic optimization occurs between increasing the amount of recovered valuable material versus the drop in product value with the decreasing product grade.
What is needed is a process for the enhanced recovery of fine particles of coal by froth flotation. What are further needed are frothers which enhance the recovery of fine particles of coal in froth flotation processes.